Abstract
The light-activated, nucleic acid-binding drugs, psoralens, were used in conjunction with a 365-nm laser microbeam to selectively bind to any nucleic acids in the centriolar region. 4'-aminomethyl-4,5',8--trimethyl-psoralen (AMT) has a high affinity for both RNA and DNA and can be shown to cause mitotic abortion when centriolar regions of prophase PTK2 cells and reacted with AMT and 365-nm laser light. Other psoralen derivatives which have a high affinity for DNA and a low affinity for RNA are not effective in blocking mitosis in dividing PTK2 cells. Examination of psoralen-bound centriolar regions by single-cell electron microscopy shows that at various times after treatment, the number of microtubules associated with the irradiated poles is much lower than in normal, dividing cells. Light-activated psoralen binding of the centriolar regions does not seem to affect the condensation or structure of mitotic chromosomes. It is concluded that there is an RNA in the centriolar region that is responsible for the formation of the spindle in dividing cells.
Highlights
Comparisons between the effects produced by these different psoralen derivatives when they are introduced to cells and bound to nucleic acids might be used to determine whether an observed effect is due to specific psoralen reaction with RNA or DNA
The majority of the radioactive counts are found in the nucleic acid fraction (4)
Fraction represents the number of cells that aborted mitosis after irradiation with 1100 J m"1 of laser light
Summary
The reaction between these drugs and double-stranded nucleic acids (e.g., DNA, rRNA) begins with the intercalation of the planar psoralen molecule into the nucleic acid helix between pyrimidines on opposite strands of the molecule. Interstrand psoralen crosslinks may be formed and have been shown to be stable under DNA denaturation conditions (Weisehahn, Hyde & Hearst, 1977). Other psoralen derivatives have a much lower binding capacity for RNA while still being efficient DNA crosslinking drugs.
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